In an article appearing in the April 1969 issue of Welding and Metal Fabrication, entitled New Equipment For Assembly of Tanks, equipment is described for internal circumferential welding of a pair of tank courses. This equipment includes a rotor having a pair of longitudinally spaced sizing rings mounted thereon. Courses to be circumferentially welded are moved on a longitudinal conveyor into position within the sizing rings. The sizing rings are hydraulically actuated and are located on each side of a circular copper backing bar. Hydraulic clamps move the courses into abutting engagement for internal circumferential tack welding. After internal tack welding, the sizing rings open wide enough to allow the tank courses to be rotated in the ring while continuous internal circumferential welding is carried out at the bottom of the ring. The copper bar is used as a backing during the continuous internal circumferential welding.
It has been found, however, that occasionally during internal circumferential welding, the weld will burn through the back-up bar and the back-up bar may become welded to the tank courses whereby an unsatisfactory weld may be obtained between the tank courses.